Created attachment 298934 [details] Screen recording STEPS TO REPRODUCE: 1. go to apple.com 2. Open the Elements tab 3. Select <body> 4. Open Layers sidebar. 5. Arrow between different rows => Flashing, stutters, etc.
<rdar://problem/30033660>
The screen recording also shows the behavior described here: https://bugs.webkit.org/show_bug.cgi?id=150551 The flashing/stuttering looks like a separate issue and not a dup.